A. Field of the Invention
The present invention relates to network devices and, more specifically, to network devices designed to implement network protocols.
B. Description of Related Art
In digital communication systems, data is routinely transmitted over processing devices in a network. In packet based networks, for example, data is transmitted in discrete quantities known as packets. A packet destined for a remote computer is typically transmitted through multiple intermediate network destinations (e.g., through routers, switches, or bridges) before reaching its final destination. At each intermediate destination, the intermediate network device may examine the packet and, based on the examination, determine the packet's next intermediate destination (or hop).
Each intermediate network device runs one or more protocols that define how the device is to forward its received packets. For example, the intermediate network device may assign the packet a high transmission priority, may apply quality of service rules to the packet, or perform error checking operations on the packet to ensure that the packet has not suffered transmission errors.
The protocols are often performed in the network devices by general purpose processors. In high performance network devices, such as high performance routers or switches, it can be difficult for these general purpose processors to keep up with the input data flow. Accordingly, specialized network processors, which implement frequently used network operations in hardware, have been developed. These specialized processors may be optimized for protocol processing.
One operation that may be implemented as a special instruction in a specialized network processor is a Cyclic Redundancy Check (CRC) error checking operation. CRC is the most common method of error detection for many data communication protocols. A CRC value is computed for a packet and attached to the packet during transmission. The device receiving the packet can verify the integrity of the packet by re-calculating the packet's CRC value and comparing it to the attached value.
Given the wide spread use of CRC based error checking techniques in data communication networks, there is a need in the art for special purpose processors that can perform CRC calculations in an efficient manner.